Mapping Mountains – Significant Height Revisions – Y Trichant – The 300m Hills of Wales

 

Aston Hill (SO 296 900) 

There has been a Significant Height Revision to a hill that is listed in the Y Trichant – The 300m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Aston Hill (SO 296 900)

The criteria for the list that this height revision applies to are:

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Aston Hill, and it is adjoined to the Cilfaesty group of hills, which are situated in the north-eastern part of South Wales (Region C2, Sub-Region C2B), and it is positioned encircled by minor roads, with the B4385 road farther to its north-east, and has the town of Bishop’s Castle towards its south-east.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was listed with a 379m summit height based on the spot height positioned at SO 29659 90041 that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Aston Hill (SO 296 900)

The summit height produced by LIDAR analysis is 380.0m positioned at SO 29663 90049, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 380.0m and this was derived from LIDAR analysis, this is 1.0m higher than the previously listed summit height of 379m, which was based on the spot height that appears on the contemporary Ordnance Survey 1:25,000 Explorer map, and importantly indicates that this map is missing an uppermost 380m ring contour.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Cilfaesty

Name:  Aston Hill

OS 1:50,000 map:  137

Summit Height (New Height):  380.0m (LIDAR)

Summit Grid Reference:  SO 29663 90049 (LIDAR)  

Bwlch Height:  341.8m (LIDAR)

Bwlch Grid Reference:  SO 28966 89594 (LIDAR)

Drop:  38.2m (LIDAR)

 

Myrddyn Phillips (September 2026)

Mapping Mountains – Significant Height Revisions – Y Trichant – The 300m Hills of Wales and Y Trechol – The Dominant Hills of Wales

 

Cefn y Coed (SO 211 934) 

There has been a Significant Height Revision to a hill that is listed in the Y Trichant – The 300m Hills of Wales and the Y Trechol – The Dominant Hills of Wales, with the summit height, bwlch height and their locations, the drop, the dominance and status of the hill derived from a Leica RX1250 survey conducted by Alan Dawson and a subsequent Trimble GeoXH 6000 summit survey and LIDAR bwlch analysis conducted by Myrddyn Phillips. 

Cefn y Coed (SO 211 934)

The criteria for the two listings that this height revision applies to are:

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

Y Trechol – The Dominant Hills of Wales – Welsh P30 hills whose prominence equal or exceed half that of their absolute height.  With the criteria for Lesser Dominant status being those additional Welsh P30 hills whose prominence is between one third and half that of their absolute height.  The list is authored by Myrddyn Phillips with the Introduction to the start of the Mapping Mountains publication of this list appearing on the 3^rd December 2015, and the list is now available in its entirety on Mapping Mountains in Google Doc format. 

Y Trechol - The Dominant Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Cefn y Coed and this was derived from the Tithe map, the Ordnance Survey One-Inch ‘Old Series’ map and local enquiry, and it is adjoined to the Cilfaesty group of hills, which are situated in the north-eastern part of South Wales (Region B, Sub-Region B2), and it is positioned with a minor road to its north and the A489 road to its south, and has the town of Trefaldwyn (Montgomery) to its north north-east.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was listed with a non interpolated summit height of c 355m, based on the uppermost ring contour that appears on the Ordnance Survey 1:25,000 Explorer map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 173m drop, based on an estimated c 356m summit height and an estimated c 183m bwlch height, with both heights based on interpolation of 5m contouring that appears on the Ordnance Survey 1:25,000 Explorer map. 

The Leica RX1250 set-up position at the summit of Cefn y Coed

However, it was not until the survey with the Leica RX1250 and subsequent LIDAR analysis and the survey with the Trimble GeoXH 6000 that the details for this hill could be accurately re-assessed. 

The Trimble GeoXH 6000 gathering data at the summit of Cefn y Coed

The summit height produced by the Leica RX1250 survey is 353.5m positioned at SO 21163 93413 and the summit height produced by the Trimble GeoXH 6000 survey is 353.6m positioned at SO 21164 93411, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 353.6m and this was derived from a Trimble GeoXH 6000 survey, this is 2.4m lower than the previously listed summit height of c 356m, which was based on interpolation of the uppermost ring contour that appears on the contemporary Ordnance Survey 1:25,000 Explorer map.

 

ills of Wales, and are reproduced below@

The full details for the hill are:

Group:  Cilfaesty

Name:  Cefn y Coed

OS 1:50,000 map:  137

Summit Height (New Height):  353.6m (converted to OSGM15, Trimble GeoXH 6000)

Summit Grid Reference:  SO 21164 93411 (Trimble GeoXH 6000)  

Bwlch Height:  184.2m (LIDAR)

Bwlch Grid Reference:  SO 20667 90868 (LIDAR)

Drop:  169.3m (Trimble GeoXH 6000 summit and LIDAR bwlch)

Dominance:  47.89% (Trimble GeoXH 6000 summit and LIDAR bwlch)

 

Myrddyn Phillips (May 2026)

Mapping Mountains – Significant Height Revisions – Y Trichant – The 300m Hills of Wales

 

Troed Rhiw Bylchau (SN 761 471)

There has been a Significant Height Revision to a hill that used to be listed in the Y Trichant – The 300m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Troed Rhiw Bylchau (SN 761 471)

The criteria for the list that this height revision applies to are:

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Troed Rhiw Bylchau, and it is adjoined to the Esgair Wen group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its north-east and south-west, and has the town of Llanwrtyd towards the east.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with 19m of drop, based on the 383m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and the 364m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Troed Rhiw Bylchau (SN 761 471)

The summit height produced by LIDAR analysis is 387.8m and is positioned at SN 76197 47177, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 387.8m and this was derived from LIDAR analysis, this is 4.8m higher than the previously listed 383m summit height, which was based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are: 

Group:  Esgair Wen 

Name:  Troed Rhiw Bylchau 

OS 1:50,000 map:  146, 147

Summit Height (New Height):  387.8m (LIDAR)                                                           

Summit Grid Reference:  SN 76197 47177 (LIDAR) 

Bwlch Height:  360.6m (LIDAR) 

Bwlch Grid Reference:  SN 76205 47017 & SN 76217 47008 (LIDAR) 

Drop:  27.1m (LIDAR) 

 

Myrddyn Phillips (April 2026)

 

Mapping Mountains – Significant Height Revisions – Y Trichant – The 300m Hills of Wales

Coed Llwyn Owen (SN 703 402) 

There has been a Significant Height Revision to a hill that used to be listed in the Y Trichant – The 300m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Coed Llwyn Owen (SN 703 402)

The criteria for the list that this height revision applies to are:

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is listed by is Coed Llwyn Owen, and it is adjoined to the Mynydd Mallaen group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with a minor road to its south and the A482 road farther to its south-west, and has the town of Llanymddyfri (Llandovery) towards the south-east.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was not included in the accompanying Hills to be surveyed sub list, as it was considered not to meet the criteria then used for this sub category.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with an estimated c 20m of drop, based on the 346m summit spot height that appears on the Ordnance Survey 1:25,000 Explorer map and an estimated c 326m bwlch height, based on interpolation of 10m contouring between 320m – 330m. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Coed Llwyn Owen (SN 703 402)

The summit height produced by LIDAR analysis is 341.5m and is positioned at SN 70382 40288, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 341.5m and this was derived from LIDAR analysis, this is 4.5m lower than the previously listed 346m summit height, which was based on the spot height that appears on the Ordnance Survey 1:25,000 Explorer map. 

 

The full details for the hill are: 

Group:  Mynydd Mallaen 

Name:  Coed Llwyn Owen 

OS 1:50,000 map:  146, 147, 160

Summit Height (New Height):  341.5m (LIDAR)                                                           

Summit Grid Reference:  SN 70382 40288 (LIDAR) 

Bwlch Height:  328.8m (LIDAR) 

Bwlch Grid Reference:  SN 70456 40324 (LIDAR) 

Drop:  12.7m (LIDAR) 

 

Myrddyn Phillips (December 2025) 

Mapping Mountains – Significant Height Revisions – Y Trichant – The 300m Hills of Wales

 

Lan Ddu (SN 716 388) 

There has been a Significant Height Revision to a hill that is listed in the Y Trichant – The 300m Hills of Wales, with the summit height, bwlch height and their locations, the drop and status of the hill derived from LIDAR analysis conducted by Myrddyn Phillips. 

LIDAR image of Lan Ddu (SN 716 388)

The criteria for the list that this height revision applies to are:

Y Trichant – The 300m Hills of Wales – Welsh hills at or above 300m and below 400m in height that have 30m minimum drop, with an accompanying sub list entitled the Sub-Trichant, with the criteria for this sub category being all Welsh hills at or above 300m and below 400m in height with 20m or more and below 30m of drop.  The list is authored by Myrddyn Phillips with the Introduction to the list and the renaming of it appearing on Mapping Mountains on the 13^th May 2017, and the Introduction to the Mapping Mountains publication of the list appearing on the 1^st January 2022. 

Y Trichant - The 300m Hills of Wales by Myrddyn Phillips

The name the hill is now listed by is Lan Ddu, and this was confirmed from the Ordnance Survey series of Six-Inch maps, and it is adjoined to the Mynydd Mallaen group of hills, which are situated in the central part of South Wales (Region B, Sub-Region B1), and it is positioned with minor roads to its north-west, west and south, and the A482 road farther to its south-west, and has the town of Llanymddyfri (Llandovery) towards the south-east.

When the original 300m height band of Welsh P30 hills were published on Geoff Crowder’s v-g.me website, this hill was included in the main P30 list with a 359m summit height, based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map.

After the sub list was standardised, and interpolated heights and drop values also included the details for this hill were re-evaluated and it was listed with 74m of drop, based on the 359m summit spot height and the 285m bwlch spot height that appeared on the Ordnance Survey Vector Map Local hosted on the Geograph website and which was entitled the Interactive Coverage Map. 

Extract from the Ordnance Survey 1:25,000 Explorer map

However, it was not until LIDAR became available that the details for this hill could be accurately re-assessed.  The LIDAR (Light Detection & Ranging) technique produced highly accurate height data that is now freely available for much of England and Wales. 

LIDAR summit image of Lan Ddu (SN 716 388)

The summit height produced by LIDAR analysis is 356.9m and is positioned at SN 71669 38863, and this comes within the parameters of the Significant Height Revisions used within this page heading, these parameters are:

The term Significant Height Revisions applies to any listed hill whose interpolated height and Ordnance Survey, Harvey or other interactive map summit spot height has a 2m or more discrepancy when compared to the survey result produced by the Trimble GeoXH 6000 or analysis of data produced via LIDAR.  Also included are hills whose summit map data is missing an uppermost ring contour when compared with the data produced by the Trimble or by LIDAR analysis.

Therefore, the new listed summit height of this hill is 356.9m and this was derived from LIDAR analysis, this is 2.1m lower than the previously listed 359m summit height, which was based on the spot height that appears on the Ordnance Survey 1:50,000 Landranger and 1:25,000 Explorer map. 

 

The full details for the hill are: 

Group:  Mynydd Mallaen 

Name:  Lan Ddu 

OS 1:50,000 map:  146, 160

Summit Height (New Height):  356.9m (LIDAR)                                                           

Summit Grid Reference:  SN 71669 38863 (LIDAR) 

Bwlch Height:  284.6m (LIDAR) 

Bwlch Grid Reference:  SN 71732 39915 & SN 71728 39925 (LIDAR) 

Drop:  72.3m (LIDAR) 

 

Myrddyn Phillips (November 2025)